This invention relates to a method and apparatus for joining together a drum body and the top and bottom ends by seaming.
A steel drum is formed by fastening a round top and bottom plate to both ends of a cylindrical body. The fastening is generally accomplished by laying together the flanges at both ends of the body and around the circumference of the top and bottom plates and then bending them over in folds. During the forming process, sealing compound is filled into the space between the folds or in the seam to prevent the leakage of drum contents therethrough.
The drum seam has an important bearing on the quality of the drum, including its strength and leakage proofness. Formed at the edges of the drum, the seam is likely to strike against other objects during handling or transportation, thereby getting loosened, deformed or cracked. To avoid such problems, many proposals have been made, and put to practical use, as to the structure of the seam, the seaming method and the apparatus.
A drum maker produces each type of drum in large quantities (for example, on the order of several handred thousands per month), using an automatic continuous production line. The seaming process constitutes the most important part of the production line. Because of such mass production by the drum making line, even a slight time saving or equipment streamlining can result in a huge profit. The increasing need for commercial distribution rationalization calls for lighter containers. This trend necessitates the development of a seaming method and apparatus which can produce container seams with adequate strength and leakage-proofness.
Generally, the seam is formed as follows. A tray-like top and bottom plate is fitted to both ends of a cylindrical body, each end having a flange extending perpendicular to the longitudinal axis of the body. A seaming chuck having a cylindrical forming face is fitted on the top and bottom plates, which are then held, and turned, with the body. A seaming roll having a forming groove is pressed against the forming face of the seaming chuck, with the edges of the flanges on the body and top and bottom plates held in the forming groove. Consequently, the flange edges are guided along the side and bottom of the forming groove and thereby are folded and seamed together.
If the pressing in the foregoing conventional method is insufficient, the resulting seam has an internal wavy shape which leaves space between folds and leads to leakage. Excessive pressing, on the other hand, causes the circular internal top edge of the seam to become acute-angled. Under the influence of excess stress, the resulting corner becomes brittle and often develops a crack when subjected to impact during transportation. This tendency is particularly great with the triple and other multi-fold seams of light-gauge sheet metal.